In a wok or deep skillet with oil, stir-fry constantly, stirring peeled and finely grated garlic and ginger (about 1 minute).
Add ground meat and stir-fry occasionally until all meat is cooked through, about 5 minutes.
Add soy sauce, sweet chili sauce, and chili powder. Stir-fry for about 2 minutes.
Pour broth into a pot, add milk, soy sauce, sugar, tahini paste or miso, and optionally peanut butter (add miso paste gradually so the soup doesn't become too salty). Stir with a whisk and heat almost to a boil.
Cook noodles according to package instructions. Chop chives, lightly toast sesame seeds in a dry pan.
All ingredients should be warmed before placing in bowls. Place noodles in bowls, then pour soup, sprinkle with meat. Sprinkle with chives and sesame, and optionally with chili flakes.